Erasing head and apparatus for magnetic recorders



O. KORNEI Dec. 26, 1950 ERASING HEAD AND APPARATUS FOR MAGNETICRECORDERS 2 Sheets-Sheet l Filed Nov. 7, 1947 Dec. 26, 1950 o. KoRNEl2,535,498

ERASING HEAD AND APPARATUS FOR MAGNETIC RECORDERS Filed Nov. 7, 1947 2Sheets-Sheet 2 By W Patented Dec. 26, 1950 ERASING HEAD AND APPARATUSFOB MAGNETIC BECOBDEBS Otto Kornei, Cleveland Heights, Ohio, assignor toThe Brush Development Company, Cleveland, Ohio, a corporation of OhioApplication November 7, 1947, Serial No. 784,563

8 Claims.

This invention relates to magnetic record transducing systems, and morespecifically to that type of magnetic record transducing systems inwhich a permanent magnet arrangement is used for preparing thesuccessive'elements of the record track for receiving a recording.

Among the objects of the invention are novel magnetic record transducingsystems including simplified permanent magnet record obliteratlng means.

Further objects of the invention include magnetic record transducingsystems in which the record obliterating means contains a minimum ofparts yet properly prepares the elements of the record track to receiveA. C. biased recordings.

The foregoing and other objects of the invention will be best understoodfrom the following description of an exemplification thereof, referencebeing had to the accompanying drawing, wherein:

Fig. 1 is a diagrammatic showing partly in section and partly inelevation of the essential elements of a magnetic record transducingassembly exemplifying the invention;

Fig. 2 shows the magnetic fields adjacent one of the erasing heads ofthe construction of Fig. 1; and

Fig. 3 is a diagrammatic explanation of the obliterating action of theapparatus of Fig. 1.

Magnetic record transducers with permanent magnet obliterating headshave been known in the art, but these heads have usually been limited toconstructions in which recordings are applied to the record trackelements with a superimposed D. C. magnetic flux. In such arrangementsrecordings are made along a relatively straightline portion of themagnetization characteristics of the record track by rst magneticallysaturating the elemental portions of the track and then biasing therecord flux signals with a D. C. flux which causes the recording tocenter about a straight portion of the hysteresis loop. This type ofobliteration and recording i5 inherently accompanied by a relativelyhigh noise level inasmuch as any slight non-uniformity in the magneticlinkage or in the record track produces large amounts oi leakage ux inthe record track. Permanent magnet preparation of record tracks forreceiving A. C. biased recordings has not been previously found verypractical beacuse the A. C. biased signals are best recorded onde-magnetized record tracks using the ability of ahigh frequencyalternating flux to collapse the hysteresis loops of the record trackelements, so that a substantially straight magnetization curve takes(Cl. P19-100.2)

l the place of the unbiased magnetization curve with its sharp knee.Unfortunately, de-magnetization is not easily effected with permanentmagnets. The normal de-magnetization requirements are at best sixreversals of magnetization with progressively decreasing flux densities,and an excessive number of magnets is required for these reversals.

The magnetic record transducing apparatus of the invention utilizespermanent magnet erasing headsI having as few as two permanent magnetsarranged to subject the elements of the record track to magnetic eldswhich leave them excellently suited for receiving recordings with A. C.bias.

Fig. l is a diagrammatic showing of the essential elements of one formof magnetic transducing system of the invention. A permanentlymagnetizable elongated record member, such as a wire or tape, is held incoiled form on the supply reel 2| and arranged for unwinding from thesupply reel and coiling onto a take-up reel 22 by suitable impellingstructures such as those shown. In moving between the reels, as forexample, in the direction of the arrow 32 for performing a transducingoperation, the record track 3| is led along a guide path over guiderollers 34. a magnetic record transducing head 36 and a capstan drive,generally indicated at 38. In the form shown, movement of the recordtrack 3| is provided by an electric driving motor 42 energized through aconnector cable 44 and provided with an on-off switch, not shown, and aconnector plug 46 which may be tted into conventional electric powersupply outlets. A rotatable shaft 48 of the driving motor 42 is shown asprovided with a plurality of pulleys 50, 5|, 52 for transmitting thedesired impelling forces from the motor to the reels 2|, 22 and capstandrive 38.

The reels 2|, 22 are shown as mounted on reel shafts 54, 55 providedwith collars 56 secured to the shaft and forming dished table-likesupports for the reels. The reels themselves are shown as including aperipheral ange portion 56 in which the record track 3| is stored and acentral hub portion 59 by which they are held on the shafts 54, 55. Acentral opening 60 in the hub portion may be arranged to fit over theupper ends ofthe shafts 54, 55 and a similar adjacent passageway 62 maybe provided in the hub 59 for receiving a drive pin 63 secured to thereel table 56 and providing animpelling connection between the reel andthe shaft. Slots 64 may be provided in the flange portion 58 forpermitting ready observation of the record track stored the reel. Thereel shafts 54, 55 are rotatably and slidably journalled in the bearingmembers l 54, 55 so that the reel drive pulleys 66, 61 may be rotated.without driving the reel shafts 54, 55, respectively. vFriction pads 12are shown as in- 'sertecl between each reel drive pulley 66, 61 and theadjoining surface of the reel tables 56 so that when the reel tables arebiased toward the corresponding reel drive pulley a frictional drivingengagement between the pulley and -the corresponding reel is effected.However, when either reel table is disengaged from its friction pad,and/or its drive pulley as by raising the slidable reel shaft on whichthe table is held, the driving interconnection between the reel drivingpulley and the reel is broken and the reel driving pulley may be freelyrotated without impelling the reel. The friction pads 12 may be of felt,cork or similar composition.

In the form shown in Fig. 1, the friction drive control is establishedby means of a pair of clutch operating slides 13, 14 guided for slidingalong the guide surface 15, and biased as by springs 11 to outer driveengaging position against stops 19. In their outer drive engagingposition the clutch slides 14, each of which has a pocket 8| in itsupper surface, receives and permits downward movement of a reel shaftsocket 83 which may be oi' spring-like construction held and biasedtoward the downward position as shown. The sockets 83 have cup-shapedportions for engagement with the lower rounded ends of the reel shafts54, 55 and in the drive engaging position in which the slide 14 isshown, the lowered positions of the sockets 83 permit the downwardmovement of the reel shafts 54, 55 under the influence of its ownweight, forv example, together with the weights of the reels mounted onthem to bring the reel tables 56 in frictional driving engagement withthe respective pulleys 66, 61, through the friction pads 12.

Actuation of either of the clutch slides 13, 14 in inward directionagainst its bias 11, forces the overlying reel shaft socket 83 out ofits receiving pocket 8| simultaneously camming it upwardly, bringing itinto engagement with and raising the associated reel shaft. Thisseparates the reel table on that shaft from the corresponding reeldriving pulley breaking the driving interconnection.

As shown, the reel driving pulleys 66, 61 are interconnected foroperation by the single driving motor 42 by a drive belt 1| loopedaround the reel shaftpulleys 66, 61 and engaging the motor shaft pulleys50, The drive belt 1| is crossed, as indicated at 84, so that the reeldriving pulleys are rotated in opposite directions. The looped portions85, 86 of the belt 1|, on opposite sides of the cross-over 84, aredriven by the motor by mounting the motor-shaft pulley within one loopso that each pulley 50, 5| engages a different arm of the same loop 85,and both pulleys are wedged toward the cross-over point. The engagedarms of the loop contact the respective motor pulleys 56, 5| on oppositesides as shown. The above driving arrangement forms a very compact andsimple assembly in which the operation of the motor impels the reelshaft pulleys 66, 61 in opposite directions and the record track may bereeled either in the forward transducing direction 32 or in a rewinddirection by simply operating one of the clutch slides 18, 1d to breakthe drive connection to the corrsponding reel, thereby permittingunwinding of the record track from the disengaged reel and impelling ofthe other reel to wind the record track thereon. Energization of thedrive vmotor t2 may be interconnected with the clutch controls as byswitches 81, 98 mounted in the path of travel of the respectiveclutchvslides 13, 14 enclosing a circuit for supplying energy to themotor 42. By this arrangement, each time one of the clutch slides 13, 14is operated inwardly to disengage a reel from the drive assembly, thedriving motor 42 is energized to impel the other reel.

'I'he record track 3| is impelled in the forward or transducingdirection 32 by the capstan 38, which in the form shown includes arelatively thin capstan shaft 81 supported against a backing bearingmember 88 and rotated as by the driving belt 89 looped over motor shaftipulley 52 and a capstan pulley shown by the dash line 90, andpositioned below the driving portion of the capstan. The capstan shaft81 is also provided with a relatively high inertia flywheel portion 9|which may be any disc-like form of relatively large diameter. Thebacking bearing 88, which is fixed and is notched, as indicated at 92,for rotatably receiving the capstan shaft 81 may be of a suitableself-lubricating construction, as for example by forming it of lubricantimpregnated porous metal such as oilite or graphite. The relativelysmall diameter of the capstan shaft 81, which may be of the order ofone-quarter inch or even less, enables it to be driven at fairly highspeeds com-parable to those of conventional electric motors forimpelling the record track 3| at the conventional linear speeds whichfor the finely divided magnetizable powder-containing record tracks isof the order of eight inches per second. Furthermore, the relativelyhigh speed of capstan rotation permits use of a flywheel 9| ofrelatively smaller mass. the flywheel 9| may be formed of threeidentical stamped metal sheets, each rotated 120 apart and securedtogether so that any inaccuracy in the stamping of the individual sheetswill be balanced out. The small rounded surface of the capstan shaft 81is brought into effective driving engagement with the record track 3| bya pressing roller 93 rotatably held on the pivoted arm 95 for movementtoward or away from the capstan shaft. In the position shown, thepressing roller 93 is set for holding the record track I'lrmly against aportion of the periphery of capstan shaft 81 so that a non-slipfrictional driving engagement effects an impelling of the record trackat a substantially constant linear speed corresponding to the speed ofrotation of the capstan. As shown, the pressing roller 93 engages thecapstan shaft in a position slightly in advance of the point of tangencyat which the successive elements of the record track 3| first reach theshaft driving surface. This brings the record track into contact with anappreciable portion of the shaft periphery, increasing the drivingcontact area and also preventing any tendency of the record track toclimb up or down on the capstan shaft because of unavoidable minordimensional inaccuracies of the impelling elements. The pressing roller93 may apply resilient pressing forces to the capstan shaft as byforming the pressing roller 93 of suitable plastic composition, or byproviding it with a resilient mounting. Because of the comparable speedsbetween the capstan shaft and the motor shaft l5 the capstan drive maymerely be Thus, for example,

effected by directly coupling the capstan shaft as by flexible couplingtothe motor shaft for rotation at the same speed.

' When the apparatus is set for transducing the driving connectionbetween the supply reel 2| and the reel shaft drive pulley 66 is open,the capstan drive is 'engaged and motor 42 is energized. The capstanwill accordingly pull the record track at the desired transducing speed,unwinding it from the supplyreel 2| and feeding it toward the take-upreel 22. The unbroken driving connection with the take-up reel 22 willcause it to wind up any slack appearing in the record track and keep therecord track in the proper record track guide path under a small amountof tension. The driving ratio between the motor shaft 48 and the take-upreel 22 is not fixed at the figure which provides the desired calculatedspeed of record track take-up, but is merely set at a low power highspeed value effective for properly coiling up the record track eventhough the take-up reel 22 is empty and only beginning to receive therecord track and its effective coiling diameter is at a minimum. Thevariable speed at which the take-up reel 22 tends to pull the recordtrack 3| is effectively dominated by the constant speed drive of thecapstan which is in substantially non-slip driving relationship with therecord track and impels the record track through the high torque smallradius of the capstan shaft 81. The take-up reel drive which has arelatively lower torque due to the step-up drive from small pulley 50 tolarger pulley 61 and through the relatively large driving radius of thereel is accordingly permitted to slip at the friction pad con- :i

nection and/or at the drive through belt 1 I. The impelled speed of therecord track during transducing will accordingly be substantiallyconstant and determined essentially by the speed of the capstan shaft81.

When the apparatus of Fig. l is set for rewinding the record track fromtake-up reel 22 to supply reel 2|, the capstan pressing roller 93 isretracted into inoperative position permitting the record track to passfreely and with very little friction over the surface of the capstanshaft 81, and the clutch slide 14 is inwardly operated. Driving motor 42is accordingly energized impelling only the supply reel 2| in clockwisedirection and winding the record back on it. The drive ratio between themotor 42 and the supply reel 2| may be similar to the step-up drivingconnection to the take-up reel 22 so that the supply reel tends to bedriven at a speed substantially higher than that required fortransducing, and in the absence of restraining forces by the capstandrive the record track may be rewound at a speed much higher than thatat which it is transduced. The rewinding time may, for example, be ofthe order of one-twentieth (1/20) or one-thirtieth (1/30) of thetransducing time.

In the form shown, operation of the magnetic recording transducer ofFig. 1 is provided by a transducer control assembly shown as aninterconnected set of push button operated control rods |0|, |02, |03,|05 and |06. These shafts are slidably mounted between guides H0, andare outwardly biased, as by biasing springs ||3, to inoperativepositions in which the control shafts |02, |03, |04, |05 and |06 areshown. The push rods |0|, |03, |04 and |06 are provided with cam lobes||4 for latching into engagement with a transversely slidable latchplate ||6 biased toward the latching position shown by spring ||1. Thelatch plate is slotted as shown at l I8 to protion in which the push rod|0| is shown, the outer face of the cam lobe ||4 is engaged by a wall ofthe latch plate bounding the slot H8. Stop projectlons |20 may beprovided on the push rods, as shown, to limit their outward travel byengagement with the wall I0.

When one of the push rods |0|, |03, |04 and |06 is actuated from theouter retracted position to the inner operated position, its cam lobe |4slides the latch plate I6 to the right against the action of its bias,and after complete penetration of the cam lobe latch plate ||6 isreturned to the position shown, effectively holding the inwardlyoperated push rod in place. At the same time, the camming action on theslide plate I6 causes it to release any other push rods that wer(inwardly latched so that non-operated rods are simultaneously returnedto their outer inactivated position.

The rods |0| through |05 are labeled, respectively, Forward, Erase,Rewind, Fast forward, Record and Stop. The Forward push rod |0I isprovided with extensions by which it is interconnected to initiate aforward or transducing operation. As shown, a pair of transducingcontrol levers |20, |2| are pivotally mounted and arranged for actuationby the Forward push rod extensions to bring the capstan into transducingdrive engagement with the record track, to break the driving connectionbetween drive motor 42 and supply reel 4|, energize the driving motorand press the record track into suitable magnetic linkage with themagnetic transducing core 3G. The transducing control lever |2| is shownas connected through link I 23 to the pivoted capstan pressing rollerarm for bringing the capstan pressing roller 93 into the engagedposition shown against the action of a retracting bias |25 when theForward push rod is actuated. The transducing control lever |20 is shownas linked to a pivoted clutch operator |21 through connector |29 so thatwhen the control lever |20 is tilted in counterclockwise direction theclutch operator |21 is tilted in clockwise direction and an arm of theoperator engages a pin |3| on clutch slide 13 moving the slide to theinward drive disengaging position in which it is shown. The inwardmovement of clutch slide 13 also closes the Contact of switch 81 andenergizes driving motor 42. An additional link |33 is connected to thecontrol lever |20 to operate a pivoted pressing pad arm |35 to urge apressing pad |36 against the action of a bias |34 toward the pole faceregion of the magnetic transducing core 36 when the Forward push rod I0|is held in the forward position shown. When the Forward push rod isretracted as by inwardly operating the Stop push rod or any of the otherpush rods, the transducing control levers |20, |2| are released andpermitted to return to inoperative position by the retracting action ofthe biasing means |25, |34 and 11 as they move the capstan engagingroller 93, pressing pad |36 and clutch slide 13 back to the normalpositions which they occupy when the transducer apparatus is notoperating. The withdrawal of the pressing pad |36 and engaging roller 93leaves a generous space alongside the transducing head 36 and thecapstan 38 along which the record track may be easily threaded in place.

For forward reeling to reach a desired portion of the record trackwithout necessitating a lengthy transducing operation, the Fast forwardaucunes push rod |04 may be moved to the inward operated position torotate a fast forward control lever las connected through iink Mt, shownbroken away, to the clutch operator 21 for breaking the drive connectionof supply reel 2| and energizing the driving motor 42 without impedingthe movement of the record track as impelled by the take-up reel 22. Therecord track is accordingly wound on take-up reel 22 at a speedappreciably higher than the transducing speed, and the selected portionof the record track will be promptly reached. If desired, an additionalswitching arrangement may be interconnected with the Fast forward pushrod |04l for rendering the ampliiler inoperative to transduce thesignals picked up and fed to it by the magnetic transducing core 36 sothat during the fast forward reeling the production of disturbing andhighly distorted sound signals is avoided.

The Rewind push rod |03 is associated through an extension with apivoted rewind control lever |42 connected for moving a rewind clutchoperator |44 through link |45. In this manner the inward portion of theRewind push rod causes the arm of the rewind clutch operator |44 toengage a pin |46 on the rewind clutch slide 14 The recording structureassociated with the Record push rod includes a magnetic erasing head |50held on pivoted arm |52 biased to the retracted position by spring |53and connected as by link |55, shown broken away, to an erasing controllever |51 cooperating with an extension of push rod |05. A set ofswitches indicated at |60 is also associated with the Record push rodfor shifting the amplifier unit connected with the transducing head 36from playback to record position. The magnetic erasing head |50comprises a pair of bar-shaped permament magnets |6I, |62 held betweenmounting wall members |64 adjustably mounted as by the pivot screw |65passing through the wall members and securing them to ears provided onthe erasing arm |52. The wall members |64 may be recessed for securelyholding the bar magnets and are provided with guide surfaces shown at|66 so that when the erasing head is moved from the retracted position,shown in full lines, to the erasing position, shown by dot-dash lines,the record track is engaged by the guide surfaces |66 so that it movespast the magnets |6I, |62 along a controllable and accuratelyreproducible guide path. Permanent magnet |6| is so located that when inerasing position the elements of the record track contact its leadingedge and then move away and past the second permanent magnet |62 with agradually increased spacing. Each magnet is polarized longitudinally andtheir adjacent ends are of opposite polarity, as indicated in thefigure, for example, to provide four magnetic fields in the record trackguide path, as indicated by the iiux lines |10, |1|, |12 and |13 in Fig.2. The relative strengths and locations of the magnets iti, |62 areadjusted so that the first eld il@ in the record track guide path isstrong enough to substantially obliterate any prior ux variations, andthe succeeding iields are of successively alternating direction andgradually decrease in strength so that the elements of the cycles of adecaying alternating magnetic iux. Such erasing action, although notgradual enough for true cie-magnetization leaves the record track in apseudo-demagnetized condition in which it faithfully records ux signalsapplied by the magnetic transducing core 36, especially when the signalsare biased by high frequency alternating flux in a manner well known inthe art. The effect of the high frequency bias appears to be not only tocollapse the hysteresis loop of the magnetizable elements of the recordtrack so that a. substantially linear magnetizing relationship isestablished for faithful recording, but also to treat the imperfectlydemagnetized elements coming from the erasing head as if they weresubstantially perfectly de-magnetized.

Fig. 2 diagrammatically indicates the operation of the obliteratinghead. In the upper portion of the gure, the magnets |6I, |62 togetherwith their ux fields |10, |1|, |12, |13 and the passing record track 3|,are schematically shown, the lower portion being a graphicalrepresentation including the curve 200, of the horizontal components ofthe respective iield intensities impressed on the successive elements ofthe record track 3| in various positions of the guide path shown in theupper portion. As a track element moves through point l of the guidepath, a relatively intense magnetic field is impressed upon it in onedirection longitudinally of the track, The intensity of this magneticiield is indicated by the peak |0 of the lower curve and is of anamphtude equal to or exceeding that of any previous magnetic history ofthe record track elements. At point 2, the magnetic eld is reversed indirection, the eld |1| being opposite to eld |10, as shown bythearrow-heads applied to the ilux lines in the upper portion of theligure. Point 3 represents the maximum zone of the nein nu to which therecord track elements are exposed, this amplitude being indicated by theminimum region of curve 200. At zone the magnetic eld is again reversed,and the track elements begin to become exposed to ilux field |12, thegreatest amplitude of which is shown at point i2 of curve 200,corresponding to location 5. Another field direction reversal takesplace at point followed by a second minimum region 1 indicated by zoneI3 of curve 200. Further movement along the record track guide pathbrings the track elements into gradually diminishing regions of iield|13, the intensity variation being shown in curve 200 between points 1and d. As can be seen in curve 200, the track elements, upon reachingposition d, have completed exposure to an entire cycle of magnetic fieldreversal and leave the magnetic head at about point 8 after beingsubjected to a second complete cycle. The successive horizontal eldintensities indicated by the maxima andminima i0, li, i2 and |3 are ofprogressively decreasing strengths.

'lhe result of the above magnetic treatment is graphically illustratedin Fig. 3, which shows a hysteresis loop 202 of the magnetizationcharacteristics of the individual record track elements. The loop isdrawn with the horizontal axis indicating the magnetizing forces H towhich the elements are exposed, and the vertical axis indicating theflux B induced in the elements upon exposure to such ilelds. As thetrack element approaches the obliterating head, it might exhibit alongitudinal iiux corresponding to the point 0 on the B-axis, therebeing no applied magnetizing iield H. The eiect oi the large fieldrecord track are passed through, two complete 7 5 intensity i@ at pointi ie to bring the track eie= ments to point 3-0I of the hysteresis loop,which point may be near the saturation point to insure uniformmagnetization no matter what the previous history of the track elementsmay have been. Thus, even if the element were exposed to `fieldintensity l with a previously contained.

flux density ranging anywhere between the points 3-02 and 3-20corresponding to maximum flux in either longitudinal direction, it willstill be brought to point I-l on the hysteresis loop. As the trackelement moves from the maximum |0 in one field direction to a maximum Ilin the opposite field direction. it is carried along the upper branch ofhysteresis loop 202, from point 3-0I through point 3-02 corresponding topoint 2 of curve 200, and brought to point 3-03 of the hysteresis loop.Because the intensity of field Ill in the guide path is less than thatof field |10, as shown by the relative amplitudes of points and I0 oncurve 200, the reversed magnetization at point 3--03 is somewhat removedi'rom the reversed hysteresis peak 3-|9.

From point 3-03 the track element is carried into the reversed field |12along a minor hysteresis loop through point 3-04 corresponding to zone 4of Fig. 2 and to point 3-05 at the maximum intensity region l. Asindicated by the lower field intensity I2, the track element is nowbeginning its second cycle of reversing magnetization. From here, thetrack element is brought through point 3-06 corresponding to' zone 6 ofFig. 2 to point 3-01 along a still lesser hysteresis loop exposed to themaximum intensity of field |13 indicated at I3. The exit from field |13brings the track element back to the zero iield axis B along the smallhysteresis loop 2-06 approximately to the point where it also exhibitsno residual flux, as indicated at 3-08.'

When the obliterating magnets areA .barshaped as shown, thelongitudinal'axes of the bars may be approximately perpendicular to eachother. Highly effective results are produced with included anglesvarying substantially from the perpendicular in either direction, atleast within the range of from about 60 to about 100. Best results for acompact type head are obtained with an included angle of 80. The path ofmovement of the record track past the magnets is also adjusted for bestoperation.

It has been found that optimum obliteration is produced when theapproach path to the first bar magnet |6| makes an angle of about 45 to90 with the axis of this bar and the departure path from the last barmagnet |62 makes an angle of about with the axis of bar |62. However,there are substantial variations in the effective range of these anglesespecially when the field provided by the magnets vary in strength, asis not infrequently found to be the case. Excellent obliteration isobtained with any approach angle 90 and with the departure angle rangingbetween about 3 and about 10.

One of the features of this obliterating head of the invention is thegenerous latitude of the approach angle which permits the elimination ofthe guide member 34 adjacent this head. The head itself may form a guidemember, the variation of record track traveling path as it unwinds fromthe supply reel 2| and comes from points moving closer to the reel axishaving no effect on the obliterating action.

Due to the variations among individual erasing heads, the operation ofthe head may not bring the track elements exactly to point @-08 of Fig.3 corresponding to the intersection of the 10 B and H axes. When this isthe case, a small amount of residual background noise appears in therecord track after the completion of the obliteration.

These variations are compensated, according to a feature of theinvention, by making a final adjustment of the obliterating head aboutits pivotal support |65 to that rotative position in which the residualnoise of the record track is at a minimum.. The effect of the adjustingrotations is that of raising or lowering residual point 3-08 along theB-axis by a small amount.

The above description has been confined to the horizontal orlongitudinal. components of the magnetic fields to which the trackelements are exposed. Inasmuch as recordings with the apparatus of theinvention are eifected by longitudinal magnetization of the trackelements, any perpendicular or transverse magnetic flux exhibited by thetrack elements are of minor consideration. However, the obliteratingheads of the invention, such as head |50 shown in Fig. 2, exhibit asuccession of perpendicularly directed fields whose maxima correspondapproximately to points 2, 4, 6 and 8. At these locations magnetic fluxis directed generally perpendicularly Ato the record track guide path.At point 2, it is directed downwardly from the lower north pole ofmagnet |6I. At point 4 it is directed upwardly to the left-hand southpole of magnet |62. At about point 6 the field is again directeddownwardly from the right-hand north pole of magnet |62, and at aboutpoint 8 the flux of field |13 is directed upwardly in its return path tothe south poles of magnets |6|, |62. The arrangement of Fig. 2 isaccordingly also effec- -tive for substantially removing anyperpendicular component of magnetic flux from the record track elementsin a manner similar to that shown for the horizontal components. Asimilar and slightly lesser extcnt of de-magnetization takes place fortransverse components. The combined result is a highly effectivemagnetic obliterating head of very simple construction.

Although the record track elements are brought to the substantially zeroresidual flux condition corresponding to point 3-08 of Fig. 3, they arenot in a truly de-magnetized condition because of the fairly abruptarrival at this condition from the highly magnetized condition at point30|, and the track elements will therefore be in a pseudo-demagnetizedcondition in which they exhibit some effects of their previous history.A minimum of three cycles of decaying magnetization reversals is usuallyrequired for an approximately perfect de-magnetization. According to theinvention, however, the magnetic record transducng system, by providinghigh-frequency alternating magnetic flux bias to the signals to bemagnetically recorded on the track elements, causes the signal recordingto take place in a manner substantially identical with that of aperfectly de-magnetized record track.

The control structure of the invention is also arranged for theprevention of inadvertent erasures or recordings, as for example, byaccidental operation of the Record push button while a record track ished in the guide path. In the form shown, the Record push rod |05 isprovided with an interacting latch projection having generallyrectangular edges |8|, |82 for @gagement iwith either side of the latchplate H6. In the outward non-operated position of the Record push rod,in which it is shown, the inner edge ist l of the latch projection itilextends behind a barlrier portion of the latch plate iii; and securelyllocks the Record push rod against inward operation either intentionallyor inadvertently. However, when a record operation is to be performedboth the Forward and Record push rods l| and may be inwardly actuatedsimultaneously by manually pushing them inwardly together. The inwardtravel of Forward push rod ibi causes its cam lobe ||4 to cam the latchplate toward the right, moving the slot l i8 surrounding the Record pushrod in front of the inner edge |85 of the latch projection andpermitting inward travel of the Record push rod. Both push rods canaccordingly be moved to their inner operated positions permitting thelatch plate ilo to be re- /tracted behind the cam lobe llt of theForward push rod and the latch projection lo@ of the Record push rod.These controls are thereby latched in place and set for a recordingoperation. Recording may be continued until any of the other push rodsare inwardly operated, camming the latch plate il@ to the right andreleasing both inwardly operated push rods lill, |05. During playbackoperation when only Forward push rod |0| is inwardly actuated, as shown,the Record push rod cannot be operated because of the engagement of thelatch plate liti with the latch projection edge iti.

The above control arrangement renders it impossible to unintentionallyoperate the Record push rod '|05 during any reeling operation. andaccordingly prevents any improper magnetic engagement between theerasing head it@ and the record track 3l. Such engagement ifinadvertently effected during a high speed reeling operation, forexample. could easily result in the erasure of a considerable length ofthe record signals and ruin the recording which may be desired to remainintact. Furthermore, the Record push rod cannot be inwardly operatedwithout an additional accompanying push rod so that even when the recordtrack 3l is held stationary in its guide path the erasing head cannot bebrought into engagement with any portionl of the record signals.

lInasmuch as the push rod ,i635 is unblocked only after some amount ofinward travel, manual operation of both push rods lil i, lilo by thefingers of one hand is quite awkward and well nigh impossible because ofthe variation in timing of the pushing impulses necessary to be suppliedby the different i'lngers. Thus, if the operating impulse applied to theRecord push rod |05 is a little too late, the Forward push rod itl willhave moved in far enough to permit retraction of the latch plate I6 intothe latching position shown blocking the latch projection |80. If theRecord push rod operating impulse is a little too early, it only causesthe latch projection edge 'll to press against the latch plate lit andincrease the friction Aof the latch plate camming action to be effectedby the cam lobe lll of the Forward push rod |0| so that a largerimpelling force must be supplied to the Forward push rod. Simultaneousoperation of the Forward and Record push rods is most simply performedby using the ngers of different hands so that the operating impulses canbe nicely timed. The rectangular latch projection edge i8! may be maderelatively short, as shown, so that only a small travel of the Forwardpush rod iol is suiiicient to unblock it. The short edge |86 may taperinto the body of the latch projection, as shown, so that after the smallunblocking action necessary, inwardly operating i forces applied to theRecord push rod |05 will assist in camming the latch plate I I6 to theright.

The magnetic record transducer of Fig. 1 is accordingly proof againstany unintentional damage to recorded signals. The erasing head |50 canonly be brought into engagement with the record track 3| by deliberateand careful operation of both Forward and Record `-push rods. Accidentaloperation is substantially impossible, even when the operator's handinadvertently presses against the record push button,

The interlocked control structure of the invention may also be operatedfor instantaneously converting from a playback to a recording operation,as for example, when it is desired to edit, erase or add comment to aprevious recording. It is only lnecessary during the playback operation,with the controls set in the position shown, that the Forward push rod||i| be held in |while another push rod, such as the Fast forward pushrod |04 or the Stop push rod |06 be inwardly operated to unlatch andpermit inward travel of the Record push rod |05. By this procedure, theeditorial material may be added while the record track is movingsmoothly and unnterruptedly along the guide path. The Stop push rod |06may merely be arranged for camming the latch plate H6 to the ri/ght forreleasing other push rods when desired. Alternatively, a switch forbreaking the energizing circuits of the motor 52, or the transduclngampliers, may be mounted for operation by inward travel of the Stop pushrod |06. With the latter arrangement, editing may be accomplished byutilizing the unblocking action of the Fast forward push rod |04, whichpermits slow forward reeling to be continued by the inwardly y heldForward push rod I0 i.

The form of the invention shown in Fig. 1 ncludes an additional Erasepush rod |02 combined with mechanism for accurately making spot erasuresat any desired portions of the recording. As shown, the Erase push rod|02 is similar to the other push rods except that it is not providedwith a cam lobe Ht. The push rod |02 is connected through spot erasinglever and link i 8| with a pivoted spot erasing arm |83 holding anauxiliary erasing head |85. 'I'he spot erasing arm |83 shown pivoted at|84 is biased, as by spring it, to a retracted position in which it iskept out fofgrnagnetic Vengagement with the record track `tirnovin'g,inits reeling guide path. Upon operatlono the erasing push rod |02 intothe inward position in which it is shown, the auxiliary erasing head |85is 'pulled into the record track engaging position shown. Although theobliterating head |50 is highly effective for preparing the record trackelements for receiving a recording, as described above, and is quitesimple in construction, it does have the drawback that the span ofmagnetic fields which it provides extends over a relatively largelongitudinal distance which may be of the order of an inch or more.Accordingly, before an element of the record track is properly erasedand is emerging 75 to an eceedingly short longitudinal portion of 13 therecord track. The construction of spot erasing head |85 shown in Fig. 1includes a plurality of thin generally bar-shaped permanent magnets |30,|9|, |92 held in a housing |95 and spaced by separator plates |91. Thethree magnets shown in this form are polarized longitudinally inalternating directions and arranged for mounting and engagementperpendicularly with the record track. The edges of the bar magnetsfacing the record track 3| may be tapered as shown at |88 so that therecord track leaving a magnet pole is exposed to a smaller flux fieldthan when approaching the same pole. The successive tapered edges |98may be spaced at increasingly greater distances from the record trackguide path, and the corresponding magnet bars may be magnetized tosmaller degrees of polarization for providing gradually diminishingfield strengths in a manner similar to that shown in connection with themagnetic obliterator head of Fig. 2. With this arrangement spot erasuresmay be made on portions of the record track as small as one-quarter (1A)of an inch, with sharp delineation between erasures and adjoiningnonerased signals. Thus, for example. the magnet bars |90, |9|, |92 maybe of generally sheet-like form having a thickness of the order ofone-sixteenth (115) of an inch or less. Ihe housing |95 may includeportions formed of highly permeable material for preventing the spreadof the `magnetic fields longitudinally along the record track guide pathand for concentration of the field produced between the recordtrack-facing pole of magnet bar |90 and the approaching portions of therecord track.

Another feature of the invention is the positioning of the spot erasinghead |85 along a portion of the record track guide path through whichthe track elements move after they have passed the magnetic transducingcore 36. As so arranged, spot erasing may be effected while theapparatus is playing back a recording, as by pressing and holding in theerasing push rod 02. The signals erased will be those signals which havejust been reproduced through the transducing core 36 a fraction of asecond earlier, so that it is merely necessary to actuate the Erasepus-h rod |02 just after the undesired signals appear in the signalreproducer, and keep the push rod down until just after the last of theundesired signals has been reproduced.

The apparatus of the invention is arranged for interlocking the Erasepush rod |02 with the Forward push rod so that erasing cannot beinadvertently effected. As sho Jn, a pivoted catch lever 2| 0 providedwith a latching nose 2|2 is positioned adjacent an extension of theErase push rod |02 and biased as by spring 2|4 to the latching positionin which the nose 2|2 prevents inward movement of the Erase push rod.Alink 2|8 connects the catch lever 2|0 with the capstan engaging lever2| associated with the forward push rod |0|, so that when the Forwardpush rod is held in inward operating position in which it is shown, thecatch lever 2|0 is pivoted in counterclookwise direction, unblocking theErase push rod. Accordingly, during a forward reeling, yas fortransducing recordings on track 3| with the controls in the positionshown, any desired portion of the record signals may be removed bymerely operating the Erase push rod to the inward position in which itis shown.

During other reeling operations, as for rewinding or high-speed forwardreeling, the Erase push rod is securely latched in inoperative positions14 so that it cannot be actuated. During the latter types of reelingoperations, spot erasures can neither be made nor monitored with anydegree of accuracy, so that the complete prevention of such erasuresensures satisfactory operation.

When it is desired to edit, or to insert substitute signals for theportion erased, as by the spot erasing head |85, audible monitoring isnot practicable, and in a great many instances the substitute signalsare not properly located, either over-running the vadjoining portions ofthe unerased signals or spaced from them by an annoying silent gap. Inaccordance with the invention, these effects are overcome byincorporating a marking mechanism for automatically applying a visiblemark to the record track at those points erased. As shown in Fig. 1, themarking mechanism includes a marking arm 2|8 pivoted as indicated at220, and provided at one end with a cam-shaped surface 220 forengagement with and operation by a cam ear 222 fixed to an extension ofthe erase push rod |02. The marking arm 2 I8 may be biased as by spring224 to a retracted limit position fixed by stop pin 22,6. The portionsof the arm adjacent the record track guide path hold a marking roller228 which may contain a marking ingredient such as ink, a portion ofwhich is transferred to the record track every time the marking roller228 contacts it. The cam surface 220 may have a projecting lobe portion2|9 bound by recessed portions arranged so that when the erase push rod|02 is in either its outer inoperative or inner erasing position, thepush rod ear 222 fits into the recesses on one side of the lobe 2 9 orthe other, but during the inward or outward travel of the push rod |02,the ear 222 engages the cam lobe 2 I9 and tilts the marking arm intomarking engagement with the record track. The record track isaccordingly marked at the beginning and at the end of every spoterasure, but not marked unnecessarily during the main body of theerasure.

For the addition of a substitute recording, the erased portion of therecord track may merely be rewound onto supply reel 2| then reeledforwardly with the apparatus set for recording, and the addition of thedesired signals commenced when the first erasure mark reaches thetransducing core 36, and terminated before the passage of the next mark.A substantial length of the record track path from the supply reel 2| to`the transducing core 36 may be arranged to be open for viewing by theoperator so that he is alerted for timely editing at a preliminaryappearance of the erasure marks in a particular zone.

For prevention of interference by the preliminary obliterating head |50,a restraining arrangement may be provided, as by including in itsoperating link |55 an extensible spring portion |54 and locking theerasing arm |52 in the retracted position shown in full lines whensubstitute signals are to be inserted.

Although three independent permanent magnets |90, |9| and |92 are shownin the spot erasing head |85, substantially the same erasing elds areprovided by substituting for the intermediate permanent magnet |9| asheet of magnetic material. Adjusting of the operating characteristicsof low coercive force the erasing head may be arranged by having themagnet |92 either with or without any of the other magnets, slidablymounted along its own longitudinal axis so that it can be clamped inplace, as by the mounting bolts shown, in the desired location in whichit l leaves a minimum background noise on the record track elements.

According to a further embodiment of the in=l vention, the magneticrecord transducing apparatus such as shown in Fig. 1, may be providedwith a single obliterating head such as that shown at i511 or at i85,and the controls may be arranged 'for keeping this head out of magneticlinkage with the record track except when erasing or recording, asdesired. For normal recording, the head may be arranged to engage therecord track in advance of the magnetic transducing core 36, and forspot erasing the same head may be moved into contact with the recordtrack after it leaves the core 3S. For such construction theobliteratinghead may, for example, be held on an arm pivoted so as to rotate andbring the core into either of these erasing positions. Linkages such asthose shown at 55 and it in Fig. l may be arranged for similarlyactuating the selectable erasing head arrangement.

The magnetic record transducing apparatus of the invention may utilizean obliterating magnetic flux iield produced by electromagnets insteadof the permanent magnets described above. The electromagnets may havemagnetically permeable cores generally similar in shape to those shownin Figure 1 for permanent magnets ii,y iti, and may carry windingsthrough which electric currents may be passed for generating the desiredux. According to this modication, when erasing is not desired, thepassage of energizing current through the erasing magnet windings-may bestopped, discontinuing the generation of flux so that the erasing headwill have substantially no effect on the record track and need not bewithdrawn in the manner shown in connection with the construction ofFig. 1. The electromagnet core materials used in this form of theinvention may be selected to have a low magnetic remanence so that whenthe energizing current through the magnet windings is interrupted, theuk immediately drops to a residual value low enough to exhibit noadverse effects on the record track movement across the magnets.

The electromagnets of such erasing head may be energized by either A. C.or D. C. current, the use of low frequency alternating current such asthe conventional 60 cycle power supplied commercially makes a veryeffective construction and enables the use of electromagnet cores havinglarger magnetic remanence. The fairly rapid alternations in the fluxfield operate to leave the. core with much less flux density than acorresponding direct current energization. To ensure a substantiallyperfect de-magnetization of the erasing head cores, the energizing ordeenergizing circuits may be arranged for exposing the cores to adecaying alternating flux of at least about 3 cycles, each time theenergizing current is interrupted. Thus, for example, the actuation ofthe obliterating operation may be connected for simultaneouslycharging'a condenser which, when thev obliterating core windings-arede-energized; Iautomatically discharges through the windings. Thisdischarge is of the nature of an oscillatory decaying alternatingcurrent having a frequency to which the capacitance and inductance ofthe discharging circuit is resonant. By selecting a dischargingcondenser of the proper capacitance, the discharging current may betuned to a point of relatively high Q or oscillation emcienoy, therebyensuring that the number o discharging cycles is large enough to producethe required gradual vperiences during reeling.

aasacee il@ decay. A simple arrangement for providing this obliteratingcore de-energizing action consists of a storage and discharge condenserdirectly connected across the windings of the obliteratingelectromagnet. The passage of energizing direct current through thewindings charges the condenser and upon opening the energizing circuitoccur. so

The iorm of magnetic record transducing apparatus shown in Fig. 1includes a limit control arrangement for automatically terminating areeling operation at predetermined points. As shown, the take-up reel 22has its hub slotted at 236 for admitting a sensing nose 232 held on alimit slide 22d guided for horizontal travel along the reel table 56, asby guides including a fixed guide 23S. The slide 234i may be biased inthe radially outward direction as by the spring 2li@ together with thecentrifugal force which it ex- The outward bias serves to urge thesensing nose 232 out against the innermost turns of the record track 2icoiled on the reel 22, and also brings the outer end oi the slide 236,shown in plan view at 2413, out far enough for engagement with astationary limit lever 255.` The end 263 may have a tapered edge 2&3 sothat when the reel 22 is rotating in counterclockwise direction, thetapered edge 26d on engaging with the limit lever 265 merely causes thelimit slide 23d to move radially inwardly. When the take-up reel 22 isrotating .in the clockwise direction, as for rewinding,

projection of the slide end 243 as by the complete unreeling of therecord track from that reel, causes a dii-'ferent non-camming edge toengage the limit lever 265, rotating it around a pivot 2536 away fromstop 202 against the action of a bias 2M. This tilting action istransmitted through a link 25@ and a trip lever 25M engaging a pin 252on the latch plate iid of the control assembly for moving the latchplate Elib to the right7 unlatching any inwardly operated control rodsand terminating the reeling.

A similar limit control arrangement is provided for the supply reel 2i.However, instead Aoi" the supply reel limit being responsive to .a

complete unwinding of the record track 'from this reel, it is arrangedfor terminating the reeling while an anchoring portion of the recordtrack still remains wound thereon. As shown in the iigure, this limitconstruction includes a tilting limit arm 25d which may be pivoted onthe reel table 56 and provided with a sensing nose portion 25d biasedupwardly as by suitably distributing the mass of the arm 25d. Thesensing nose 256 may be located in a position where it engages some ofthe turns of the record track 3i a short distance removed from theinnermost turns through one of the slots @il in the flange portion ofthe reel. The outer portions of the limiting arm 25d are shown asincluding a depending lip 2Q@ having a tapered edge 262 ior co-actionwith a second limit lever 265 pivoted as at 26d and urged toward a stopposition against pin 26W by spring 26S. The forward reeling limit lever265 is connected through link 2l@ with a second pivoted trip lever 2i2arranged for engaging a pin 2id on the latch plate HG.

The forward reeling limit is accordingly similar to the rewindingreeling limit associated with take-up reel 22. When the supply reel 2iis rotated in the clockwise or rewind direction, the tapered edge 262 ofthe limit arm 256, upon engaging the limit lever 265, merely causes thelimit arm 254 to tilt and ride over the limit lever. However, when thesupply reel 2| is rotated in the counterclockwise or forward reelingdirection and a sumcient amount of the record track is unwound to permitupward movement of the sensing nose 256, the tilted limit arm 254 bringsa non-camming edge of the ear 260 into engagement with the forward limitlever 265, rotating it and thereby unlatching any inwardly held pushrods stopping the reeling.

The forward reeling may be arranged'so that even at the high speedwithwhich fast forward reeling is eiected, the arresting action is completedbefore all of the record track is unwound. In this way the rewinding maybe readily made by simply operating the rewind push rod |03 without anyfurther record track threading or anchoring operations.

It will be apparent to those skilled in the art that the novelprinciples of the invention disclosed herein in connection with specificexemplications thereof will suggest various other modifications andapplications of -the same. It is accordingly desired that the inventionshall not be limited to the specific exemplifications described herein.

I claim: Y

1. -In a magnetic record transducing apparatus for magneticallyrecordingby transducer head means signals of the audio frequency range with asuperposed alternating bias eld of at least twice higher frequency on a.flexbile elongated permanently-magnetizable record track guided andimpelled in a transducing forward direction along a predetermined guidepath and for reproducing the recorded signals with said head meanslocated along said path: an erasing head comprising permanent magnetmeans having at least three permanent magnetic poles, a base, meanssecuring said permanent magnet means to said base forming a unitarystructure, means adjustably connecting said erasing head to said recordtransducing apparatus adjacent the guide path for erasing andmagnetically substantially neutralizing elements of said track beforethey reach said head means while recording; said erasing head comprisinga permanent magnet structure free from any extraneous magnetizingwindings and having an elongated exposed pole region of said at leastthree poles past which said track moves along said guide path forproducing solely by said permanent magnet structure along an erasingpath section of said guide path extending in front of said poles anerasing magnetic flux eld of at least three oppositely Y directedportions decaying in intensityin the forward direction of said guidepath, starting with an initial portion of intensity sufficient tomagnetically saturate track elements passing therethrough and endingwith an end portion of low intensity effective in reducing themagnetization of passing particles to a negligible level, a portion ofsaid permanent magnet means constituting a guide element positioned inthe said initial maximum intensity portion of said erasing flux iieldengaged by and guiding the track along said erasing path section forsaturating track elements coming into engagement with said guideelement.

2. In a magnetic record transducing apparatus as claimed in claim 1,said apparatus also having control means actuable to cause saidtransducer head means to carry on with said track either a recordingoperation or a reproducing 18 operation in each of which operations saidtrack moves at a transducing speed, said control means being alsoselectively actuable to cause said track to be impelled at a highernon-transducing speed in a non-transducing operation, said control'means also including setting means having setting elements selectivelysettable to either one of a plurality of settings including a recordingsetting or reproducing setting whereby said control means is selectivelyset to cause said apparatus to perform either said recording operation,or said reproducing'operation, means movably connecting said erasinghead to said transducing apparatus, means biasing said erasing head toremain and return to retracted position in which said record track issubstantially free from the action -of said erasing field and beingmovable to an erasing position in which it subjects said track to saidera-sing action, and means operative in response to setting of saidsetting mean to a recording setting for causing said erasing head to bemoved to and retained in said erasing position while said setting meansis in a recording setting only, said erasing head being actuated toreturn to said retracted position in response to actuation of saidsetting means from said recording setting to any other setting.

3. In a magnetic record transducing apparatus for magnetically recordingby transducer head means signals of the audio frequency range with asuperposed alternating bias field of at least twice higher frequency vofa flexible elongated permanently-magnetizable record track guided andimpelled in a transducing forward direction along a predetermined guidepath and for reproducing the recorded signals with said head meanslocated along said path: an erasing head comprising permanent magnetmeans having at least three permanent magnetic poles, a base, meanssecuring said permanent magnet means to said base forming a unitarystructure, means adjustably connecting said erasing head to said recordtransducing apparatus adjacent the guide path for erasing andmagnetically substantially, neutralizing elements of said track beforethey reach said head means while recording; said erasing head comprisinga permanent magnet structure free from any extraneous magnetizingwindings and operative to produce solely by said permanent magnetstructure along an erasing path section of said guide path an erasingmagnetic flux field comprising a plurality of oppositely directedunidirectional field portions; said apparatus also having control meansactuable to cause said transducer head means to carry on with said trackeither a recording operation or a reproducing operation, in each ofwhich operations said track moves at a transducing speed, said controlmeans being also selectively actuable to cause said track to be impelledat a higher non-transducing speed in a non-transducing operation, saidcontrol means also including setting means having setting elementsselectively settable to either one of a plurality of settings includinga, recording setting or a reproducing setting, or to a nontransducingsetting whereby said control means is selectively set to cause saidapparatus to perform either said'recording operation, or saidreproducing operation, or said non-transducing operation, means movablyconnecting said erasing head to said transducing apparatus, meansbiasing said erasing head to remain in and to return to a retractedposition in which said record track is substantially free from theacaccesses 19 tion ci said erasing eid, means for matins said erase headto an erasing position in which it subjects said track to said erasingaction; and means operative in response to a setting oi said settingmeans to a. recording setting fot causing said erasing head to be movedto and retained in said erasing position While said setting means is ina recording setting only, said erasing head being actuated to return tosaid retracted pontion in response to actuation or seid setting meansfrom said recording setting to any other setting.

4. In a magnetic record transducing apparatus es ciaimcd in ciaim i, caamagnet structure computing two distinct genereiiy @cramped permanentmagnet members having 'soies at their ends.

e. in a magnetic record trmducing apparati@ es claimed in claim 7, thenoise ci? one ci the two magnet members beine from seid mth.

es claimed in claim 1, one pcie of seid mamet structure constitutingvthe guide element.

5. in a magnetic record transducing aoparatus as claimed in claim 4,said magnet structure comprising two distinct generally bar-shapedpermanent magnet members having poi-ee at their ends.

6. In a magnetic record transducmg apparatus as ciaimed in ciaim 5, thepoles of one oi' tite two magnet members being spaced from said erasingpath.

7. In a magnetic recordtransfiucing apparenze UTET@ iOim.

The foiiowing references are of record in the ie of this patent:

sra'rns en Number Name Bate Vitliiii Oct. 2e, w3?, iii@ Hickman Jing; t,i937 2,1ii5i Smith Jan. ii, i933 @BMGN PATENTS Number Country Date22,463 Smtzeriand Ang. 3i, 119139 322,252 @i June 2i, 1920 @$3,022France inne 22, wie

